Audio/visual unsynchronised

(at around 21 mins) When Newt's mother is calling in the mayday, she is heard saying "Alpha zero two four niner" repeatedly, but the second time she says it her mouth is saying something else. (Special Edition only)

Character error

Before the marines' final stand in Operations, their motion trackers cannot tell if the aliens are on the same level. Therefore the aliens' ability to surprise and slaughter the marines hinges entirely on character error. Ripley references the earlier scene, in which they examined the floor plans, with the possibility that the aliens came in through something they missed or was not in the plans, that being the space above the suspended ceiling vents. By this time, the stress of the situation could have caused everyone to forget this, unlike the calmer floor plan scene.

Burke tells Bishop to keep the facehuggers alive for return to the company labs. Given the harm they would inevitably have caused, complying would seem to be a violation of Bishop's programming. If not, then Bishop is being remarkably candid, meaning Burke didn't tell him to keep that order secret.

Newt tells Ripley that nobody calls her Rebecca except her brother Timmy. But Timmy does call her Newt when trying to calm her down while they wait inside the surface rover. Timmy could have simply lapsed in his familiar habit at that moment.

When the crew wake up, in the background, you can hear Sergeant Apone in the background telling Crowe and Wierzbowski to get up from the Cryo Chamber even though Crowe is already seen walking about in front of Spunkmeyer.

Continuity

When Ripley tries to break the glass in the med lab there is a scuff mark on the glass before her first swing. After this finishes, the mark disappears and we see Ripley actually making the mark with her second swing. (This goof was digitally corrected for the blu-ray edition)

(at around 1h 45 mins) In the elevator escape scene where Hicks gets acid sprayed, he holds his gun in front of his face and turns his head to the left. Any acid burns he got would have been to the right side of his face. As they fight to remove his melting chest armor, there are no acid marks on his face. When they leave the elevator, the acid burns are on the left side of his head, instead of the right side.

In Alien, the computer displays have an old-fashioned "teletype" clicking noise when they show data on their screens. However, when the screen in the Nostromo shuttle comes to life at the beginning of Aliens, the display looks and sounds more modern like the other computer screens seen later in the film - even though 57 years have passed and the equipment in the shuttle has not been touched all that time.

(at around 53 mins) When Burke, Ripley and Lt. Gorman first enter the colony building, they pass through the pouring rain outside and get soaking wet. A few seconds later, inside the building, their clothes and Ripley's hair are dry again. (This scene is part of the extended edition)

(at around 3 mins) In the very beginning of the movie when the salvage crew is cutting into the lifeboat, in the close-up shot the plasma cutter makes a cut at a right angle but in the long shot when the door falls, there are no right angles on the door they cut. So the shape of the door being cut does not match between the close-up and long shots.

The first dropship has the "Bugstomper: We endanger species" logo just beneath the cockpit. When the APC rolls around the corner and is loaded onto the dropship we see the other side (pointing to the right) of the dropship and the logo faces the same way as on the pointing to the left side. In every other scene the Bigstomper logo has been correctly painted in a reverse manner it still faces toward the front end of the dropship.

When the Marines and Ripley first encounter Newt, Drake fires wildly at Newt's scurrying silhouette as Hicks uses his own pulse rifle to deflect Drake's line of fire up and into the corridor wall. But there is no visible damage to the wall after Drakes ceases firing.

After an alien smashes a hole through the triangular windshield on the APC during the escape from under the cooling tower the windshield is then shown with an unbroken windshield as it exits on to the planet surface.

(at around 54 mins) The monitors for each of the marines' head-mounted cameras are identified by each marine's last name and first initial, located in lower right-hand corner of the monitor (e.g., Hicks D., Apone A., Hudson W., etc.). This is true for Vasquez' monitor (Vasquez J.), with one exception. While in the processing station and after Apone says, "Uh, roger. That's a two-one-six.", her monitor reads "Vasquez.".

Near the end when Ripley is on the dropship, she is seen arming
herself. We see her grab a flamethrower from the weapons rack. She then lays a pulse rifle on the deck. Next she pulls a pulse rifle from the rack, and lays down a flamethrower. (The 2010 Blu-ray is slightly re-edited to remove this error.)

When Hicks first gives Ripley the locator wristband, the locator can be heard beeping at a steady rate. However, near the end of the film when Ripley finds the wristband while trying to rescue Newt. The locator beeps much faster, even though the wristband is about the same distance away as it was in the Ripley/Hicks scene earlier.

(at around 1h 5 mins) When Vasquez shoots the alien that suddenly comes out of hiding near Drake as the Marines are escaping the processing plant, its blood splashes across his entire body, but only the left side of his body is shown as being affected.

(at around 56 mins) When Gorman, Burke, and Ripley are discussing the firing of weapons under the primary heat exchangers as the marines are first going to sub level 3, Gorman's headset moves around on his hat, sometimes sitting below the rim of his hat and sometimes above the rim of his hat, finally toward the end it is completely under his hat.

When Hudson gets out of his cryotube on the Sulaco, he has several sensor pads attached to his torso. In the next shot (after Apone asks him if he wants him to bring him his slippers) the two upper pads are no longer there, even though Hudson didn't remove them.

Towards the end, when Ripley is on her way to rescue Newt, we see the pilot light on Ripley's flamethrower. When she pauses to drop a flare there is no pilot light. The next shot shows the pilot light again.

As Ripley and the marines are escaping through the ventilation tunnels, when Vasquez is attacked by an alien from above, we see briefly that her hair has become ruffled. In the next shot when she has the alien trapped with her foot, her hair has become smooth and even again.

When Hicks is sprayed by acid blood during the colony escape, some of it gets on his skin and causes only relatively minor scarring despite the fact that in both the first film and this one, it is established that the aliens' blood can burn holes through metal flooring that is much more durable than soft human tissue.

While Frost is falling after being set on fire and falling over railing, just before the shot cuts away, in the bottom left corner you can see a crewmen moving and a boot sticking out from the shadows.

(at around 26 mins) After Spunkmeyer loads the missile, he calls "Clear behind!" and walks the power loader backward. A thick cable can be seen attached to the loader's left foot. (The loaders are supposed to be free-standing.)

Factual errors

When the dropship is released, it is shown to be falling immediately as if in full gravity. However, since the Sulaco is placed on a stationary orbit, the dropship should remain in place upon releasing the clamps. An additional burn would be necessary to initiate deorbiting.

At the end of the movie, the compound explodes and the survivors escape in a shuttle. We see that brightness of the explosion shines on their face. But in fact, the explosion and the light source is behind, so there's no way their sight would be affected by the brightness.

The landing sequence is incorrect. The dropship is seen accelerating while deorbiting, such acceleration would send it to a higher orbit. Deorbiting needs deceleration from the orbital speed. The dropship should have fired retro-rockets or it should have turned backwards to use the main thrusters for deceleration.
Moreover, if the Sulaco is exactly above the colony (as stated in the novelization), the dropship should have done a vertical drop (relative to the planet) or should have completed a full orbit while descending to end up right above the colony.

When the drop-ship is lowered into the airlock, it is held in place by a number of arms lowering it from the ceiling. Presumably the inner airlock doors close round these arms, which continue to hold it prior to release. However the outer airlock doors open below the ship just a few seconds later, without enough time for the airlock to have been evacuated to anything close to a vacuum.

Miscellaneous

Sergeant Apone (Al Matthews) can be heard being referred to as "Top" by his Marines. This term is used when referring to Master Sergeants (E-8), but his chevron clearly indicate the Marine rank of Gunnery Sergeant (E-7).

The marines are supposed to be "Colonial Marines" but yet they have the patch of the American Flag on their uniforms (one of these patches is clearly visible on Gorman's uniform). Their full title is actually "US Colonial Marines" so an American flag would not be surprising. According to the Aliens VS Predator universe, the United States as we know it right now has evolved by the time of the movie (assuming that the movie is in the AVP universe), it's known as the "United Americas", so the American Flag patch on the Marines' uniforms makes no sense as is Burke and Bishop mentioning some American States (i.e., Wisconsin and Nebraska respectively).

Incorrectly regarded as goofs

The inquest had gone on for "three and a half hours", yet no one mentioned that LV-426 had been colonized for over twenty years. Given the fact that the board needed to hold Ripley accountable for the willful destruction of the Nostromo for insurance reasons, they obviously felt it was in nobody's best interest to broach the subject.

(at around 1h 29 mins) When Ripley goes back to medical to join Newt, she lays her rifle on top of the bed and then lays down on the floor beside Newt. Moments later she looks to break the glass but finds her rifle laying on a table on the other side of the glass. The scene makes it clear that Burke entered while she and Newt were asleep and laid down the opened containment cylinders with the facehuggers inside of them; it's fairly obvious that he moved her rifle out of the room as well (note Ripley's expression when she sees her rifle).

It is often believed that everyone stands up comfortably inside the APC yet are taller than it when standing outside of it. In reality, everyone hunches over inside the vehicle except for the much smaller Vasquez.

In the Special Edition, as the Dropship heads to the planet, Cpl. Hicks appears to be asleep. As the ship enters the atmosphere and the marines get ready to deploy, he is clearly awake. In the next shot he is still asleep. Finally Apone says "Somebody wake up Hicks." This is all meant to demonstrate how seasoned a soldier Hicks is: that he can "sleep" through the drop. At no point is he ever actually asleep, he's just very relaxed. He opens and closes his eyes as the conversation interests or disinterests him. Apone is simply making a joke about this.

The shuttle pilot's seat has ejection handles. Since the shuttle travels between atmosphere & space, wouldn't ejection would be more dangerous than remaining on-board, both for the pilot AND passengers? Not necessarily so - pilot ejection would still be practical for atmospheric flight, and a sufficiently advanced seat could include a deployable bubble or shell for surviving space or even atmospheric re-entry - In the early 1960s, NASA designed a number of concepts for ejection seats that could be used to escape from a spacecraft in Earth orbit and allow an astronaut to safely re-enter the atmosphere. Passenger or payload recovery would be more problematic. But again, an integrated system of the future might provide reasonable survival capability.

(at around 1h 25 mins) After Vasquez cuts a hole in the conduit to allow Bishop to crawl to the transmitter, the metal cut out segment falls into the conduit pipe through the hole. When Vasquez replaces the cut out piece, it should fall through the hole again but doesn't. This is because the piece tilted at an odd angle once it was cut free.

(at around 1h 2 mins) When the ammo bag that Frost had been holding explode, Crowe is thrown against a wall, breaking his neck, yet Hicks reports that "Wierzbowski and Crowe are down". He should have said "Crowe and Frost are down", as Wierzbowski is still alive at this point.

When the marines respond to the fire alarm in the medical bay, to save Ripley and Newt, immediately after shooting the second face-hugger, Corporal Hicks calls for "Paxton" instead of Bill Paxton's character's name, "Hudson." Hicks actually does say "Hudson," but the way in which he yells it may cause some people to interpret it as "Paxton."

When Apone tells the Marines to hand in their magazines, Vasquez hides a pair of what look like batteries with 1/4 inch phone jacks and gives one to Drake - these are ostensibly the battery packs for the smart guns they are carrying, which supposedly fire some kind of plasma projectile at their target. But moments after Vasquez says "Let's Rock!"and begins firing, you can see a conventional ammunition belt hanging from the smart gun (which is actually a heavily disguised MG42 machine gun).

(at around 2h 10 mins) At the end of the film as Ripley is closing the sleep chamber for Bishop, you can clearly see his IV pack has an expiration date of 08/87. However, Aliens takes place in 2179, so the expiry date could be 07/2187.

In the original "Alien," it's established that the Nostromo investigates LV426 after receiving a transmission from an alien ship. By the time the planet was colonized, the transmission had stopped broadcasting. In the Special Edition of this film, the derelict ship from which the transmission was broadcasting is shown to be heavily damaged, presumably from lava flows, which obviously has damaged the transmitter.

In Alien, LV-426 is adjacent to a huge planet with Saturn-like rings (which it probably orbits). Such is its size, it can even be viewed from the surface (i.e. when the Nostromo crew investigate the alien ship). The ringed planet is never seen in this film, either from space or from the surface of LV-426 because James Cameron simply chose not to depict it from any angle.

While it may seem that there is no reason for Bishop to sleep in cryostasis like the rest of the crew since he is not on the mission covertly (like Ash was in Alien), it is plausible that he is programmed to pass for human by default.

Portable satellite phone existed in the 20th century which could call satellites in orbit. Were the story set in a timeline respective to our own, this would make the need to use the colony's transmitter to contact the Sulaco rather unnecessary, but James Cameron set the story within the fictional universe established by Alien, which had not depicted such satellite phones as being commonplace.

Near the end, as Ripley is trying to escape after rescuing Newt, Ripley pauses when she realizes she's in the Queen's lair. As she turns slowly to view the Queen, Ripley's and Newt's head are facing in opposite directions as they hug each other, but when the camera angle changes during that slow turn, both heads are suddenly looking in the same direction at the Queen. The cut could have occurred several seconds later.

When Bishop is piloting the drop-ship remotely, he mistakenly says, "E.T.A. 16 minutes." While an estimated time of arrival for a flight plan requires a specific time during the day, e.g. 12:16 EST, or 20:16 Zulu and Bishop should have said, "E.T.E. 16 minutes," it is highly likely that Bishop simply did not care about formalities or proper procedure at this point in time given the futility of the situation.

Just before the shootout scene which leads to Hudson's death, Newt says "Ripley, let's go." You can hear a noticeable English accent when she says these words. Actress Carrie Henn was living in England with her parents at that time and was obviously playing herself. She speaks like this throughout the film and James Cameron did not see fit to correct it.

Given that the chest-burster's gestation period from implantation of the egg to eruption through the host's chest seems to be on the order of hours, the Colonial Marines never should have found a still-living, impregnated colonist on LV-426, because the Marines requiring cryo-sleep to reach the planet implies a weeks- to months-long journey -- so all of the colonists (except for Newt) should have been long dead and the chest-bursters born by the time the Marines arrived.

During the inquest scene, Ripley tells the panel that Kane said he saw "thousands of eggs" in the derelict alien ship on LV-426, and she repeats the word "thousands" to impress this. In actual fact, Kane never said that at all. When he went into the hold of the derelict ship in Alien, he simply said he thought he was in a cave of some kind that was filled with "leather objects like eggs or something." He did not give a number. Later, after he regains consciousness aboard the Nostromo, he doesn't seem to remember anything at all about the experience and so could not have gone into any more detail about it.

When fighting with the Alien queen, Ripley opens the inner hatch of the airlock. She then opens the outer hatch, but without closing the inner one first. Normally the air in an airlock would be cycled whilst both doors are shut.
It should not be possible to have both doors open at the same time, and there should be safeguards to ensure this. It might be possible that there would be an over-ride, but this would presumably require entering an authorisation code, which Ripley clearly doesn't do.

Revealing mistakes

(at around 21 mins) When Bishop is "doing the thing with knife" the scene is sped up to give the impression that Bishop is lightning fast. Apone can be seen rocking his head back and forth, also at a ridiculous speed.

(at around 4 mins) When the salvage crew shines a light onto Ripley's face while she is sleeping at the beginning of the movie, her right eyelid twitches. Although people's eyelids twitch all the time when they are asleep, Ripley is is frozen in cryogenic suspension - not merely asleep.

(at around 21 mins) Before Bishop begins doing "the thing with the knife", knife marks from earlier takes or practices are visible on the table in the exact spot where his and Hudson's hands are yet to be placed.

Just before Ripley rescues Newt from the cocoon, she kills the parasite coming out of the egg and one of the aliens charges at her. As it is moving down and towards Ripley, wires can be seen on top, helping to move it along.

Whilst Ferro is piloting the drop-ship down to the planetoid, on the computer screen showing navigation, the characters at the bottom of the screen are back to front, indicating that the scene had been mirrored.

(at around 1h 45 mins) When Ripley is preparing the M41 rifle with the flamethrower she is seen loading a new cartridge of ammo in the rifle as the counter runs up to 95. Once the elevator doors open the counter reads 42. She hasn't yet fired a shot.

(at around 1h 6 mins) During the escape in the APC, containers fall from the overhead storage, yet none of them strike Gorman anywhere near his head - they later say he has a concussion, and leaves the medlab with blood from his wounds showing through his bandage. In fact, only one of the containers strikes Gorman on the right arm and they way in which they fall indicate they are empty, clearly not enough force to knock him out cold.

In the queen's egg chamber shortly before Ripley "demonstrates" her flamethrower to the queen, an alien egg on the right of the screen, closest to Ripley's left leg, wobbles obviously. It's clearly very light and hollow.

When the APC is first entering the atmospheric processing plant, it drives towards the camera down a hallway. The floor of the hallway is wet, and the right wall is shiny, and you can see reflections of the actors, showing that they are trotting behind the APC (and not actually inside it), then walk to the front, as if they had just exited the vehicle. If you watch carefully, some of the marines emerge from behind the APC and run along the side opposite the door, but not enough time elapsed for them to have emerged from the door, run *back* along the APC, around the back, and to the front.

This has been hidden somewhat in the later releases (Director's Cut, Special Edition, Remastered Edition, etc.) with flare from the headlights and a shorter cut.

After the climactic battle with the Queen, Ripley plunged into the airlock, and as she is unbuckling from the loader we see her t-shirt is torn at the right shoulder. She then is presented to be climbing vertically out of the airlock. The torn t-shirt torn flaps are clearly pointing horizontally in front of her, indicating that gravity is pulling in front of her rather than below her.

When Ripley asks Gorman "What do those pulse rifles fire ?", Gorman replies "10 millimetre explosive-tipped caseless. Standard light armour-piercing round.". Later, in the sequence in the air-ducts, as Vasquez is firing back along the duct to defend their retreat, empty shell casings can clearly be seen being ejected from the breech of weapon onto the duct wall as she shoots. Caseless ammunition, as the name suggests, doesn't have a shell casing to eject; it's an integral part of the ammunition and either exits the barrel along with the round itself or is consumed by the act of firing. This is because the the marine's prop weapons were made by combining modified Thompson SMGs and Benelli shotguns, both of which use conventional "cased" ammunition.

When the sealed dropship is shown head-on just about to drop, we can see it is a model: there are numerous differences in its appearance from the full-sized dropship. With the model, the windshield is fogged and dirty with no internal light; the full-sized version's windshield is clean, with internal light. The painted "01" decal on the model is much less precise. The headlights on model are rounded rectangles; the headlights on the full-sized dropship are circular.

The scenes showing the Marines inside the APC show that the vehicle is tall enough for them to stand upright inside of it. However, when the Marines exit the APC when inside of the atmosphere processor, it is obvious that they are quite a bit taller than the vehicle, making that one a scale model.

Spoilers

The goof items below may give away important plot points.

Audio/visual unsynchronised

After the first contact with the Aliens at the processing station and Drake is killed, Vasquez is being held back by Hicks near the door of the APC. He yells that Drake is gone and she says, "No he's not," but her mouth does not move in sync with the line.

Character error

Despite having argued at her inquest that the derelict contains "thousands of eggs," when Ripley and the marines are trapped on LV-426 and discussing their situation, she wonders how there could have been enough eggs in the atmosphere processing station to impregnate over one hundred colonists. Obviously the entire colony did not travel out to the derelict. Newt's father was the first host; the next may have been members of a rescue team, who were all brought back impregnated, from one of whom a Queen was birthed.

Continuity

(at around 2h 10 mins) After the Queen falls down the airlock, the sharp end of her tail is missing (obviously unintentional, and overlooked or not repaired by the crew). The tip is back on moments later as she's tumbling through space.

When the queen grabs the loader in the final fight scene, she topples it over first smashing the yellow rotating beacon light on the top then pulling it in the airlock, but when the loader is shown in the air lock the light is undamaged and operating.

Incorrectly regarded as goofs

In the Special Edition, although Newt's parents don't have any descending gear like the kind Kane used to access the deep egg hold in the first film, they do not enter the ship in the same location. You can clearly see that they enter it through a crack that has formed in the ship's hold, which would put them closer to the egg chamber, if not right where it is.

(at around 2h 10 mins) At the end of the film, when Newt asks if they are going to sleep all the way home, she suddenly speaks with a noticeable English accent. Actress Carrie Henn was living in England with her parents at that time and was obviously playing herself. She speaks like this throughout the film and James Cameron did not see fit to correct it.

In the Special Edition, Newt's family finds the derelict alien ship not by chance, but as a result of orders given by the colony technician seen in Operations, whose associate mentions the "Mom and Pop survey team." He himself was given orders by "some honch in a cushy office on Earth" who told him to "go look at a grid reference." That honch, of course, is Burke, whose directive Ripley discovered in the colony log.

Revealing mistakes

When Bishop saves Newt from being sucked out of the airlock, part of Lance Henriksen's real torso can be seen beneath the false one, emerging from a hole in the floor. (James Cameron acknowledges this error on the DVD commentary; the goof was digitally corrected for the 2010 Blu-ray release.)

When Vasquez shoots the alien which causes Drake's death, the exact shot of the alien exploding and spraying its acid blood everywhere is used again when the second pair of remote sentry guns (in the special edition) are firing away. In fact, it's used twice in this scene in quick succession.

The wire that pulls the Queen's tail out of Bishop's chest is visible, but it is *not* the white strand that most people assume to be it. The strand is just an unidentified piece of material pulled out *by* the tail, and can be seen to snap and fall away. The wire itself is a monofilament visible for a brief moment before the tail begins to emerge.

When Ripley is firing grenades into the Queen's ovipositor, after one of the last explosions, an intact, yellow chicken egg yolk is clearly seen sliding out of the wound. (It is even more obvious in one of the Quadrilogy's DVD featurettes.)